Method and apparatus for producing stepped hollow shafts or stepped cylindrical hollow members by transverse rolling

ABSTRACT

The invention relates to a method and a device for transversely rolling stepped hollow shafts or cylindrical hollow parts from a pipe. The invention achieves the object of rolling stepped hollow shafts of the most varied dimensions and also of greater lengths in a flexible manner from a pipe using a small number of simple tools. In accordance with the invention, the object is achieved by virtue of the fact that rolling tools which can be radially advanced and are disposed in a planet-like manner around the workpiece are used to roll the contour of the transition from a central diameter in one portion of the workpiece to the central diameter in the adjacent portion by means of co-ordinated control of the radial advance of the rolling tools and the axial feed of the workpiece, and a mandrel head having an outer diameter which is adapted to the smallest inner diameter of the two portions is disposed underneath the rolling tools.

The invention relates to a method and a device for transversely rolling stepped hollow shafts or cylindrical hollow parts from a pipe. In particular, pipe blanks for manufacturing divided and undivided pipe stabilisers for motor vehicles can be produced in an advantageous manner. They are characterised by virtue of the fact that they have variable diameters and wall thicknesses in regions over their longitudinal axis, which on the one hand leads to a reduction in component weight and on the other hand permits optimal usage of the installation space available. Furthermore, the load-adapted cross-sections permit a uniform tension distribution and thus optimal usage of the material used. When utilising the invention for the pipe-stabiliser application, further advantages can be achieved by eliminating wall thickness fluctuations in the pipe used and by improving the material quality of the pipe surfaces by stretching any decarburization regions present and so-called “phosphate edges”.

Various solutions for transversely rolling stepped hollow shafts or hollow bodies or cup-shaped hollow parts over a mandrel are already known.

In accordance with DD 99 521 A or even DE 199 05 038 A1, the blank is axially compressed between wedge-shaped tools with inner forming tools at the same time during the rolling process and is rolled out starting from the centre to form a double-sided cup-shaped hollow body. The outer contour of the inner forming tools (mandrels) corresponds to the inner contour of the hollow body.

In the broadest sense, the solutions for rolling bearing seats and outer toothings (EP 0 248 983 A1 or DE 199 58 343 A1) or inner toothings (e.g. U.S. Pat. No. 5,765,419) are classified in this group of transverse rolling with profiled mandrels or transverse rolling tools.

Longer hollow shafts are reduced substantially only in wall thickness on a continuously cylindrical mandrel, either continuously (WO 02/55226 A1 or DE 20 04 444 C3) or in sections (DE 101 15 815 A1). The last solution is a type of transverse rolling of a stepped hollow shaft. However, only the outer diameter of the hollow shaft is stepped in sections. The inner diameter is unchanged over its entire length and corresponds to the outer diameter of the mandrel.

In order to produce a pipe-shaped stabiliser for motor vehicles by forming, rotary swaging can be utilised. However, it is not particularly productive in spite of high technical outlay.

It is the object of the invention to provide a solution with which stepped hollow shafts or cylindrical hollow parts with the most varied dimensions and also longer lengths can be rolled in a flexible manner from a pipe using a small number of simple tools.

The object is achieved in accordance with the invention by virtue of the fact that by means of rolling tools which can be radially advanced and are disposed in a planet-like manner around the workpiece the contour of the transition from a central diameter in one portion of the workpiece to the central diameter in an adjacent portion is rolled by means of co-ordinated control of radial advance of the rolling tools and axial feed of the workpiece and a mandrel head having an outer diameter which is adapted to the smallest inner diameter of the two portions is disposed underneath the rolling tools.

It has been found that these transitions can also be rolled without the assistance of a mandrel whose outer profile corresponds to the inner profile of the transition. At the beginning of a transition from a large central diameter to a smaller one, the outer periphery of the mandrel head does not lie against the inner periphery of the workpiece at the instantaneous forming site. Only towards the end of this transition and during rolling of continuous portions having a constant inner diameter does the mandrel perform its typical function. For this purpose, it is disposed underneath the rolling tools.

Tests have demonstrated that it is possible to produce a pipe-shaped stabiliser for motor vehicles with two regions, which are stepped on the end side, and one long central part, which is reduced in diameter and wall thickness, from a pipe having a length of 1.6 m, ca. 22 mm outer diameter and a wall thickness of ca. 4 mm. The process is very productive. It is fundamentally possible to produce the stabiliser in a clamping system.

The friction between the workpiece and the mandrel head is restricted to a minimum. This is achieved on the one hand by a relatively short mandrel head and on the other hand by means of a clearance fit, which is typical for displacement, between the outer and inner diameters of the mandrel head and the workpiece. Moreover, in addition to this clearance a further clearance of at least 0.1 mm is preferably provided which promotes forming and is to be defined as flexing clearance.

The forming procedure is further assisted by virtue of the fact that the workpiece is mounted in support rollers.

Preferably, three support rollers are disposed in each case in one plane in a planet-like manner around the workpiece and are mounted in a stand. They can be radially advanced onto the workpiece. The stands are displaceable in parallel with the workpiece axis. At least one stand is disposed in a stationary manner in proximity to the rolling tools. Particularly in the case of longer workpieces, at least one further stand is provided which preferably moves simultaneously with the workpiece end, to which it is allocated. Overall, the support rollers serve to absorb the “transverse forces” which result from the forming procedure and which are not neutralised by the rolling tools and the active part of the rolling mandrel. Such remaining transverse forces also occur primarily during rolling of the transitions. Moreover, they support the weight of the workpiece parts which protrude over the active (engaged) part of the rolling mandrel.

Preferably, the forming procedure is performed using rolling tools which have a smoothing shoulder and a forming shoulder, wherein preferably the free edge of the smoothing shoulder is rounded off with a radius of 0.5 to 3 mm. Primarily, the short transitions are rolled with this edge. In order to roll transitions which on one portion are short on both sides, the workpiece is preferably turned.

Portions having greater wall thicknesses and consisting of materials which are difficult to form (e.g. high-tensile steels) are heated prior to rolling.

Further features in accordance with the invention are described in the claims and in the exemplified embodiment.

The invention will be demonstrated hereinunder in several exemplified embodiments. In the drawings,

FIG. 1 shows a plan view of a device in accordance with the invention,

FIG. 2 shows an enlarged section of FIG. 1,

FIG. 3 shows the section “Z” of FIG. 2,

FIGS. 4 a to 4 h show the stepwise formation of a pipe into a hollow shaft.

The device for transversely rolling stepped hollow shafts from a pipe as shown in FIG. 1 has an approximately cross-shaped outline in the plan view shown in FIG. 1. A rolling spindle drive 4, a rolling mandrel bearing 7, a rolling mandrel 8, the workpiece 1, support rollers 9, a clamping device 6 and an axial rolling carriage 5 are disposed in parallel with the axis of the workpiece 1 (the pipe to be formed or the resulting hollow shaft) from right to left.

Rolling tools 3 are provided at the forming site. They are mounted in radial rolling carriages 2. These rolling carriages can be displaced transversely with the respect to the workpiece 1. The rolling tools 3 are radially advanced therewith. For this purpose, they have a dedicated, preferably hydraulic, drive. The rolling tools 3 are driven about axes in parallel with the workpiece axis by means of the rolling spindle drive 4. During forming, the workpiece 1 is pulled with the axial rolling carriage 5 to the left and at the same time is rotated with the rolling tools 3. The clamping device 6 for clamping the workpiece 1 is located on the axial rolling carriage 5. The forces for pulling the workpiece 1 are applied against the rolling tools 3 by two hydraulic pistons which are disposed in a pivotable manner in the axial rolling carriage 5.

As shown more clearly in FIG. 2, a carriage guide 11 is disposed underneath the workpiece 1. Stands 12 which each have three support rollers 9 are disposed in a displaceable manner on this carriage guide. The support rollers 9 surround the workpiece 1 in a planet-like manner and can be advanced radially onto the respective outer diameter of the workpiece 1. The stand 12 a in direct proximity to the rolling tools 3 is stationary. The stands 12 b which are further away from the rolling tools 3 move with the workpiece 1 (see the double arrow under the stands 12 b). Their spaced interval from the rolling tools 3 changes continuously during forming. The movement direction of the workpiece 1 is shown on the left-hand side by an arrow.

Any remaining transverse forces applied to the workpiece 1 immediately adjacent to the forming site and in each case at the furthest spaced interval from the forming site are absorbed by the support rollers 9.

As shown in FIG. 3, the free edge of the smoothing shoulder of the rolling tool 3 is rounded off with a radius r.

FIGS. 4 a to 4 h illustrate the sequence of forming a hollow shaft which has multiple steps in its central part.

In each case, the workpiece 1 is clamped in the clamping device 6 and is pulled the distance of a feeding path s_(ax). The rolling tools 3 are advanced radially by the distance s_(r). The respective path length is indicated by the length of the arrow. The direction is given by + and −. During axial feeding, + in the drawing denotes the movement to the left (in the direction of tension of the clamping device 6). The radial advance of the rolling tools in the direction of the workpiece axis is denoted by +, and the opposite direction is denoted by −. Rolling mandrels 8 a to 8 c which have an outer diameter corresponding to the respective smallest inner diameter of the workpiece are used. The mandrel head has not been illustrated.

In FIG. 4 a, the workpiece is still the original pipe. It is already clamped. Rolling tools 3 and rolling mandrels are not in engagement.

In FIG. 4 b, a first transition from the previous diameter to a smaller central diameter is rolled. The rolling tools 3 are advanced with +s_(r). The workpiece 1 is pulled the distance of a small axial feed path. The large diameter mandrel 8 a is disposed underneath the forming site. At the beginning of the transition, the inner periphery of the workpiece 1 is not yet supported by the mandrel 8 b.

In the next step (FIG. 4 c), the position of the rolling tools 3 is no longer radially adjusted. The workpiece is pulled the distance of a relatively long feed path (see arrow size of +s_(ax)).

In the steps 4 d and 4 e (cf. FIGS. 4 d and 4 e), further step-formation similar to that performed in steps 4 b and 4 c is carried out but with the medium diameter rolling mandrel 8 b.

FIGS. 4 f and 4 g illustrate on the one hand a repetition of the above-described forming steps with the smallest diameter rolling mandrel 8 c. A feature of FIG. 4 g is that a conical transition is rolled. A small axial feed +s_(ax) is coupled with a negative small advance −s_(r) of the rolling tools. The rolling mandrel is still located underneath the rolling tools 3 but at the instantaneous forming site is still only in radial proximity to the inner periphery of the workpiece 1.

In the final stage, FIG. 4 h, the hollow shaft is completely rolled. The rolling tools are disengaged.

In practical tests, a hollow shaft was rolled from an approximately 1.5 m long pipe consisting of 34MnB5 having an outer diameter of about 25 mm and an wall thickness of about 4 mm. In a central portion (ca. 400 mm long) and at the two ends (ca. 200 mm long), the pipe was stepped by about 2 mm at the outer diameter. The wall thickness of the stepped parts was reduced by about 1 mm. The forming portions were heated. The average rolling temperature was 600° C. 

1) Method of transversely rolling stepped hollow shafts or cylindrical hollow parts from a pipe with rolling tools which can be advanced radially and are disposed in a planet-like manner around the workpiece, axial feed between the workpiece and rolling tools and a mandrel, wherein the rolling tools are used to roll the contour of the transition from a central diameter in one portion of the workpiece to the central diameter in the adjacent portion by means of co-ordinated control of the radial advance of the rolling tools and the axial feed, and a mandrel head having an outer diameter which is adapted to the smallest inner diameter of the two portions is disposed underneath the rolling tools. 2) Method as claimed in claim 1, wherein the rolling tools comprise a cylindrical smoothing shoulder and a conical forming shoulder. 3) Method as claimed in claim 1, wherein in addition to the clearance required for the axial mobility of the mandrel head in the workpiece, a flexing clearance of at least 0.1 mm is provided between the outer diameter of the mandrel head and the corresponding smallest inner diameter of the workpiece. 4) Method as claimed in claim 1, wherein the workpiece is externally supported against transverse forces at least one site by support rollers. 5) Method as claimed in claim 1, wherein the workpiece is turned when changing from one portion to the next. 6) Method as claimed in claim 1, wherein the rolling tools are turned when changing from one portion to the next. 7) Method as claimed in claim 1, wherein prior to rolling a portion the workpiece is heated in the region of the next forming portion. 8) Device for transversely rolling stepped hollow shafts or cylindrical hollow parts from a tube with rolling tools which can be radially advanced and are disposed in a planet-like manner around the workpiece, devices for producing an axial feed between the workpiece and the rolling tools and a mandrel, wherein the control of the radial advance of the rolling tools and the control of the axial feed between the rolling tools and the workpiece are coupled together by a program control and a mandrel head having the outer diameter which is adapted to the smallest inner diameter of the two portions is disposed approximately below the rolling tools. 9) Device as claimed in claim 8, wherein the rolling tools comprise a cylindrical smoothing shoulder and a conical forming shoulder. 10) Device as claimed in claim 9, wherein the free edge of the smoothing shoulder is rounded off with a radius r of 0.5 to 3 mm. 11) Device as claimed in claim 8, wherein the mandrel consists of a mandrel head and a mandrel shaft which is reduced in diameter with respect to the mandrel head. 12) Device as claimed in claim 11, wherein the mandrel head length corresponds approximately to the axial width of the rolling tools. 13) Device as claimed in claim 11, wherein the mandrel head is cylindrical. 14) Device as claimed in claim 8, wherein in addition to the clearance required for the axial mobility of the mandrel head in the workpiece, a flexing clearance of at least 0.1 mm is provided between the outer diameter of the mandrel head and the corresponding smallest inner diameter of the workpiece. 15) Device as claimed in claim 8, wherein the workpiece is mounted between support rollers which can be radially advanced. 16) Device as claimed in claim 15, wherein in each case three support rollers are disposed in one plane in a planet-like manner around the workpiece and these three support rollers are mounted in a stand. 17) Device as claimed in claim 16, wherein the stand is disposed in an axially displaceable manner in a guide (11) lying in parallel with the workpiece axis. 18) Device as claimed in claim 17, wherein at least one stand also travels at the axial speed of the workpiece part, to which it is allocated. 19) Device as claimed in claim 18, wherein the travelling stand is allocated an axial drive and the control thereof is connected to the program control. 20) Device as claimed in claim 16, wherein at least one stand is disposed in a stationary manner in the vicinity of the rolling tools. 21) Device as claimed in claim 8, wherein the rolling carriage (5) is axially displaceable. 